The aim of this project is to characterize an appropriate model system in which to explore the anatomy and physiology of an efferent pathway from a circadian oscillator to an anatomically discrete unit that expresses an overt rhythm. A system of coordinated circadian oscillators and the oscillations they regulate is important in the maintenance of functional integrity in multicellular organisms, including humans. This proposal details a series of studies in which electron microscopic examination of cockroach ommatidia will be carried out to demonstrate the occurrence of a circadian rhythm in morphological changes. Changes in position of screening pigment granules in retinula cells relative to the rhabdom will be an obvious anatomical feature used to assay for the presence of a circadian rhythm. Ommatidia to be examined will be taken at six-hour intervals over a three- day period from cockroaches, Leucophaea maderae, held under constant conditions of darkness and temperature (i.e., free- running). In addition, the impact of transecting the optic lobe either proximal or distal to the lobula on the expression of this circadian rhythm will be assessed in an effort to locate the putative oscillator that governs the rhythm of these anatomical changes. These studies are patterned after those used to localize the circadian oscillator responsible for generating the rhythm of retinal sensitivity to light in the cockroach L. maderae. Having localized a putative circadian oscillator and an overt rhythm it regulates, exploration of the efferent neuroendocrine pathway from the oscillator to the discrete anatomical unit (retinula cell) expressing the oscillation will be initiated. A gas chromatographic - mass spectrometric technique to identify endogenous neurochemicals, and a biological assay system using the isolated optic lobe to test for putative neurochemicals that can mimic natural changes in ommatidial morphology, currently being developed in this laboratory, will be used.